The overall goal of this research is to determine the function and regulation of cytochromes P450 (CYP) as potentially associated with developmental effects of chemicals in fish. Various chemicals elicit severe abnormalities in development of cardiovascular, neural, and connective tissue sin fish, often culminating in mortality. Understanding these effects of chemicals in fish will require knowledge of CYP, given the central role of CYP in oxidative biotransformation of xenobiotics and many regulatory molecules. There is direct knowledge of the identify and function of multiple CYP in very few fish species and only one (the killifish Fundulus heteroclitus) that is used extensively in environmental toxicology. Our recent cloning efforts (as part of an existing SBRP project) have identified 10 CYP genes in F. heteroclitus. These include members of subfamilies previously known in fish (CYP1A, CYP2K, CYP3A), subfamilies we have newly identified in fish (CYP1B1), and genes representing entirely new CYP subfamilies (CYP2N, CYP2P). Several of these enzymes are potential targets in the effects of chemicals on developmental processes or reproduction. We shall determine functional properties and expression of multiple CYP in developmental stages and the interactions with chemicals common at Superfund sites. 1. CYP will be expressed with P450 reductase and evaluated for activity with developmental toxicants (AhR agonists; xenoestrogens) and regulatory molecules (steroids; retinoids). 2. Temporal and cellular patterns of CYP expression will be determined, emphasizing blastula and gastrula stages, during which there are critical windows for effects of some chemicals. 3. Effects of chemicals on CYP expression during development will be determined and compared with localization of other enzymes and function of Fundulus CYP1B as compared to CYP1A will be examined in fish that are resistant to TCDD, vis-a-vis responses in sensitive populations, as related to potential roles of CYP in susceptibility. Although the Specific Aims outline studies on multiple CYP, several aspects will focus more closely on CYP1A and the new first CYP1B, given their potential involvement in the pronounced developmental effects of aryl hydrocarbon receptor agonists. Studies will be performed primarily with killifish although some aspects will be examined also in zebrafish (Danio rerio); both species are important developmental models.